Control circuit for chopped feeding

ABSTRACT

A control circuit is provided for chopped feeding which circuit receives at its inputs an alternating voltage and at its outputs delivers a direct chopped voltage. The choppers are controlled by comparing an error voltage with a sawtooth signal on a fixed frequency generated by a unijunction transistor, whose output is connected to a bistable for channel switching.

Grandin de lEprevier et a1.

[11] 3,823,336 [451 July 9,1974

CONTROL CllRCUllT FOR CHOPPED FEEDING Inventors: Ludovic Grandin dellEprevier,

Belfort; Andre Achille Brecy, Danjoutin, both of France Societelnclustrielle Honeywell Bull, Paris, France Filed: Dec. 29, 1972 ApplNo.: 319,825

Assignee:

US. Cl! 3211/18, 307/140, 321/43 Int. Cl. H02m 7/00 Field of Search321/18, 43, 47; 307/140 References Cited UNITED STATES PATENTS 12/1968Schaffer 321/18 6/1970 Huber 321/18 X 5/1973 OSullivan 321/47 PrimaryExaminer-William M. Shoop, Jr. Attorney, Agent, or Firm--Fred Jacob [57]ABSTRACT A control circuit is provided for chopped feeding which circuitreceives at its inputs an alternating voltage and at its outputsdeliversadirect chopped voltage. The choppers are controlled bycomparing an error voltage with a sawtooth signal on a fixed frequencygenerated by a unijunction transistor, whose output is connected to abistable for channel switch- 6 Claims, 3 Drawing Figures PATENTEBJUL91914 SHEEI 3 0F 3 BACKGROUND OF THE INVENTION The present inventionrelates to a control circuit, intended especially, but not exclusively,for chopped power feeding in which thefeeding is carried out in two orseveral channels.

It is the function of chopped feeding to supply the load circuit, whichmay be for instance a logical circuit, with a direct voltage during atime t, in the course of a period T. The voltage V obtained at theoutput of the feeding circuit is given by the formula V K'E, wherein Kis the form factor defined by the relation t/T (T being the period ofthe alternating current at the feeding-input terminals and E being thevoltage available at the output terminals for feeding when the circuitis closed).

The form factor is generally determined by the closing of a chopperelement during the time t. This element connects the input and theoutput terminals of feeding, and is for instance, a transistor. Whensignificant power is to be furnished to the load circuit, theinput-output of the feeding is connected, as is known, by two channelssuch that each transmits the current only during half the time t, whichprevents prohibitive dissipation in a single channel during the time I.There are then, two circuit breakers.

The problem solved by the invention consists in the controlling of eachof the circuit breakers during a set time t/2, in the course of a periodT. Various solutions to this problem have been proposed in the past. One

such solution consists of using a determined part of a signal of avariable period as a control signal for the circuit breakers, in otherwords, one cuts off a fixed portion of a signal whoseduration isvariable which results in a signal of variable duration. In a knowndesign this subtraction is'done by hysteresis in a magnetic core.Unfortunately, this leads to a substantial loss of energy in the core.

One of the objectives therefore, of the present invention is theselection of a switching period based on a circuit with fixed frequency.The operation of the assembly is thus, markedly simplified.

SUMMARY OF THE INVENTION I According to the present invention thecontrol circuit for chopped feeding includes a voltage source to beconnected with the output of the feeding through at least onecircuit-breaker element. Said circuit receives at its inputs, on the onehand, a negative feedback sig- According to another characteristic ofthe invention, the generator of the sawtooth signal, as mentioned above,includes a conductor and a unijunction transistor. The unijunctiontransistor partly supplies a sawtooth signal, and partly supplies apulse for each tooth.

Since the circuit breakers are controlled by pulses the number of themagnetic circuits necessary is reduced and the total output is thusincreased.

BRIEF DESCRIPTION OF THE DRAWING Other characteristics and advantages ofthe invention will evolve in the course of the following description ofvarious forms of embodiment, taken with reference to the accompanyingdrawing, wherein:

FIG. 1 is a generalized diagram showing a chopped feeding circuit;

FIG. 2 is a schematic diagram showing the sawtooth oscillator asutilized in the circuit of. FIG. I; and

FIG. 3 is a diagram showing a control circuit accord ing to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The feeding, properly speaking,is represented on the right side of FIG. 11 and includes two terminals 1to which an alternating voltage Ve is applied. The primary 3 of atransformer 2 is linked to these terminals and the center point of thistransformer is connected with the ground potential. The secondary 4,whose center point is also grounded, is tied to an output terminal 7 bymeans of two rectifiers 5 and 6, and a coil 8 which with the condenser 9form a filter cell. The desired voltage signal V,- is disposed betweenthe terminal 7 and the ground.

The feeding as such is not part of the invention, and the transformer 2which was mentioned, although useful, is not indispensible. Theinvention concerns the control of the choppers l0 and 111 at desiredtimes. For this purpose a negative feedback signal CR is transmittedfrom the feeding output to one of the inputs of the comparator 12, whichsupplies at its output an error voltage which is applied to a secondlinear comparator 113. A sawtooth signal is applied to the second inputof the comparator 13 which is generated at 14, and which will beexplained below. An output signal of the stage 14 is applied to abistable 15, each of the two outputs of which is connected with one ofthe inputs of the two AND gates 16 and 17, while the comparison signalstemming from the comparator I3 is applied to the input.

This circuit operates in the following manner. The comparator l2simultaneously receives at its inputs the negative feedback signal CR,and the reference signal. The comparator ll2 is a differential amplifierthat furnishes at its output an error, or control signal e. The sig nale is compared in the stage 113 with a sawtooth signal.

When the voltage of the sawtooth signal is higher than the voltage ofthe error signal, the comparator 13 sends a pulse to the input of thegates 16 and 17. The duration of this pulse is determined, on the onehand, by the period and the form of the sawtooth, and on the other hand,by the voltage of the signal e. It is then possible by varying thisvoltage e to select a time t, for the closing of one chopper. The choiceof one or the other of the choppers wand 111 is carried out by means ofthe pulse appearing at the output of the unijunction transistor duringdecay of the voltage of the sawtooth signal.

FIG. 2 illustrates the sawtooth signal generator of the stage 14. Itconsists basically of a unijunction transistor 20, a condensor 21, apotentiometer 22 and a resistor 23. The transistor 20 and the resistor23 are tied to a feeding source +V The resistor 24, connected with thebase of the transistor 20, on the one hand, and with the ground, on theother hand, is a bias resistor. When the circuit is placed under voltagethe condensor charges according to a law which in a first approximationmay beconsidered linear and which depends on the time constant RC, Rbeing adjustable. By setting the potentiometer 22 one makes sure thatthe charging time t, of the condensor 22 is constant. When the voltageat the terminals of the condensor 21 reaches a set value the condensordischarges over the unijunction transistor 20 by furnishing to the baseof the latter (the low value of the resistor 24 should be kept in mind)a pulse which is transmitted to the bistable 15.

On the other hand, the desired sawtooth'signal S appears at the pointcommon to the resistors 22 and 23 and is applied to one of the inputs ofthe comparator 13. As mentioned above, the comparison of this signalwith the error voltage produces a pulse of variable size.

FIG. 3 shows a diagram of a control circuit according to the inventionin which the bistable has not been included. However, the referencecharacters of the elements already mentioned have been retained. Thecomparator 12 is a differential amplifier consisting of two transistorsNPN 26 and 27, to the bases of which the negative feedback signal CR andthe reference sig nal r are respectively applied. The error signal e istaken from the collector of the transistor 26 and applied to the base ofthe transistor 28. The condensor of weak capacitance is intended tofilter the noise that may appear.

The previously mentioned sawtooth signal is applied to the baseof thetransistor 29 while the error voltage e is applied to the emitter of thesame transistor. The transistors 28 and 29 are 'PNP transistors. Whenthe potential difference between the emitter and the base is suitable,the transistor 29 is conducting and a pulse appears at its collectorwhose duration is a function of the level relation between the referencevoltage and the sawtooth. After amplification, this pulse constitutesthe signal of the variable form factor F desired, which is sent off overone or the other channel through the intermediary of the bistable 15 soas to altematingly form the choppers l0 and 11.

The difierent elements of stage 14 are presented in detail in FIG. 3.The presence of the bistable 15 is, by the way, only necessary in thecase of double altemating feeding. The switching-pulse signal from thebase of g the unijunction transistor 20 is amplified by the transistor32 and sent to the terminal 25- of the-bistable input.

Thus, the present invention makes it possible to generate at a fixedfrequency a signal whose duration and voltage may be modified withoutaffecting the frethe circuits and makes their operation a great dealmore easy. The use of a unijunction transistor, on the other hand, whichis accomplished in the circuit according to the invention, avoids theapplication of a large number of active components, and thereby reducesthe costs.

What is claimed is:

1. In a chopped feeding system including a voltage source and at leastone chopper connected to said voltaseswssanq hay n an pytpiitatw l shiti ss ted to produce pulses of selected frequency and of selected timeduration, a control circuit for controlling said chopper to produce saidpulses and which comprises:

means connected to the output of said feeding system for producing anerror signal indicative of deviation of said pulses;

sawtooth generator means for producing sawtooth voltage output which isof said selected frequency; and

comparator means connected to said error signal and to said sawtoothvoltage output for producing control pulses at said selected frequencyand of said selected duration to control said chopper.

2. In a system as defined in claim 1 wherein said sawtooth generatormeans is a relaxation oscillator including a capacitor and a unijunctiontransistor for discharging said capacitor and wherein said comparatormeans comprises a pair of transistors connected in parallel and havingrespective base electrodes connected respectively to said error signaland to said sawtooth voltage output.

3. In a system as defined in claim 2 wherein said comparator means alsoincludes a transistor having a base electrode connected to thattransistor of said pair thereof to whose base electrode said sawtoothvoltage output is connected.

4. A circuit according to claim 1 wherein said sawtooth generator meansincludes a condensor and an unijunction transistor.

5. A circuit according to claim 2, characterized in that the choppedfeeding system includes two choppers, the pulse appearing in the outputof the unijunction transistor during the discharge said condenser beingapplied to the input of a bistable element for the selection of one orthe other chopper.

6. A circuit according to claim 3, characterized in that the outputsignal of said comparator means is applied simultaneously to one of theinputs of two AND gates, the second input of each of the two gates beingconnected with one of the bistable outputs, each of the outputs of saidgates being connected with a chopper.

1. In a chopped feeding system including a voltage source and at leastone chopper connected to said voltage source and having an output atwhich it is desired to produce pulses of selected frequency and ofselected time duration, a control circuit for controlling said chopperto produce said pulses and which comprises: means connected to theoutput of said feeding system for producing an error signal indicativeof deviation of said pulses; sawtooth generator means for producingsawtooth voltage output which is of said selected frequency; andcomparator means connected to said error signal and to said sawtoothvoltage output for producing control pulses at said selected frequencyand of said selected duration to control said chopper.
 2. In a system asdefined in claim 1 wherein said sawtooth generator means is a relaxationoscillator including a capacitor and a unijunction transistor fordischarging said capacitor and wherein said comparator means comprises apair of transistors connected in parallel and having respective baseelectrodes connected respectively to said error signal and to saidsawtooth voltage output.
 3. In a system as defined in claim 2 whereinsaid comparator means also includes a transistor having a base electrodeconnected to that transistor of said pair thereof to whose baseelectrode said sawtooth voltage output is connected.
 4. A circuitaccording to claim 1 wherein said sawtooth generator means includes acondensor and an unijunCtion transistor.
 5. A circuit according to claim2, characterized in that the chopped feeding system includes twochoppers, the pulse appearing in the output of the unijunctiontransistor during the discharge said condenser being applied to theinput of a bistable element for the selection of one or the otherchopper.
 6. A circuit according to claim 3, characterized in that theoutput signal of said comparator means is applied simultaneously to oneof the inputs of two AND gates, the second input of each of the twogates being connected with one of the bistable outputs, each of theoutputs of said gates being connected with a chopper.